Bifocal lens.



A. J." CROSS. BIFOOAL LENS.

APPLICATION rrman MAY 10, 1012.

1,06 3,421 o Patented Junwfi; 1913.

ANDREW JAY CROSS, OF NEW YORK, N. Y.

BIFOCAL LENS.

To a7] 107mm it may concern Be it known that I. Aunnrw JAY CROSS, of thecity, county, and State of New York, have invented a new and usefulImprovement in Bifocal Lenses, of which the following is a full.clearyand exact description.

My invention .relates to improvements in bi-fo -al lenses such as are.used for spectacles and eye lasses.

It is well (nown that a bi-focal lens at its best, has its limitations,because it is a compromise in an attempt to combine reading glasses anddistance glasses in one, to obviate the necessity of using two sets ofglasses. As generally constrl'lcted they are open to -certainobjections, chiefly because it is difficult to secure coincidentprincipal axes for the lens, some forms ofthem are expensive, difficultto change or repair, and moreover the reading surface of the glass isusually cemented on, and in many cases the cement becomes cloudy andimpairs vision. Some kinds of these lenses are not easily made orrepaired by an ordinary lens grinder or repairer, and often, and in factusually, the reading segment or glassis cemented on over the distanceglass, and while the lens -may be scientifically correct, the mode ofattachment causes a ledge orshelf on the upper edge of the readingsegment, which collects dust and dirt, and which even when care istakento keep it. clean,will result in an objectionable streak which confusesvision.

In an attempt to overcome some of the above difiiculties, bi-focalglasses are sometimes made in which the distance glass is recessed, anda segment of reading glass of greater density set into the recess, fusedin place, and then ground sn'rootli so as to leave a surface flush withthe distance glass. This makes a handsome lens, but is open to thedifficulty that it often has double prin cipal axes or centers andtherefore'not so scientifically correct as the older types of singleaxis centered bi-focal lenses, also be cause the curvature of therecessed segment is apt to be such to produce more or less aberrationof. light and of course unsatisfactory vision.

The object of my invention is to overcome all these difficulties, andproduce a simpler,

more correct, not too conspicuous a glass, in

which there is no danger of obscuring the reading surface by cement, andin which the reading surface can be made of any desired size, and thelens easily made or repaired.

Specification of Letters Patent.

Application filed May 16,1912.

PatentcdJune 3, 1913.

Serial No. 697,618.

Further, to produce a lens in which the 0bjectionable ledge or shelfabove referred to is d1spensedwith,ai 1d an overhang produced instead,in which there is no danger of dust collecting. Furthermore, by means ofmy improvements, the stud straps of the glasses serve to bind the twolens members together and make them exceptionally secure, and whenconstructed as described below, a mono-centric, single principal axisbi-focal lens is much easier to produce, and it will be understood thatunless an optically monocentric or single principal axis lens isproduced, great confusion and discomfort to the wearer or user canresult. This will appear clearly from the description which follows.

Reference is to be had to the accompanying drawings forming a part ofthis specification, in which similar reference characters indicate acorresponding part in all the views;

' Figure 1 is a front elevation'of a pair of spectacles provided with myimproved lenses. Fig. 2 is a detail front elevation. of the readingglass. Fig. 3 is a front elevation of the distance glass. Fig. 4 is avertical cross section of the complete lens, and Fig. 5 is a verticalcross section showing the segment glass thinned at its principal axis.

In carrying out my invention I make the glass 11 which is the readinglens, the full size of the glass or lens to be produced, and of theright properties for near vision, that is for reading, while the lenssegmentor glass 12 shown in Fig. 3, is to be thin at its center orprincipal axis and of the right quality to form a distance glass whencombined with or laid over the lens or glass 11.

Those skilled in the profession will understand that it is a simplematter to combine the segment glass 12 with the reading glass 11, sothat the combined glasses will produce a lens having the right opticaleffect for distance vision. There is nothing new in this phase of thelens. To illustrate the above, Fig. 4 shows the lens glasses 11 andsegment glass 12, as essentially flat, While Fig. 5 shows the segmentglass thinned at the center, and the glass 11 as a double convex glass,but as stated above, the peculiar configuration of the members 11 and 12will of course vary as desired. It is new, however, to make the readingglass the full size of the lens, and to cut out a portion of thedistance segment glass 12 as shown at 13, so as to leave an unobstructedsection through this part of the reading glass. The result is that noshelf is produced on the reading lens which corresponds to that part ofthe glass 11 exposed by the recessed portion 13 of the glass 12, andconsequently there is no projecting shelf of the reading glass, butsimply an overhang which will not collect dust or dirt. Moreover, bymaking the twov members of the lens the full size, it will be seen thatthey may or may not be cemented by the usual clear cement, but that thepart of the lens for reading, which as stated is that part of the glassexposed through the recess 13, is always left entirely uncemented, andtherefore clear and free from any. possible discoloration or otherinterference. It will be further seen that by the constructiondescribed, the two members of the lens are held together by the studstraps 14 and 15, which can be of any usual kind, and which greatlystrengthen the security of the lens where frames are not used. As shownthe stud straps 14 form a part of the nosepiece, and the stud straps 15connect with the bows, but on eyeglasses the parts 15 would be dispensedwith. In grinding the lens an optical center or principal axis isproduced on the distance glass 12, at the highest point of the recess13, and on the reading glass 11 at the junction of the two lens members,thus producing a single optical center on 11 and 12 at this point.

From the foregoing description it will be seen that the lens is verymuch more inconspicuous than a lens which is produced by cementing on areading segment of a size,

corresponding to the opening of part 13 over the distance glass, also itcan be seen that the reading part or opening in the segment 12 can bemade of any desired size, and that the members of the lens'can be veryeasily ground, adjusted, repaired and assembled. It will also be noticedthat it is easier when making the lens in this manner, to bring theprincipal axes ofthe members in coincidence with each other, which is avery important matter in lens manufacture. It will "be further observedthat the member 11 can be placed on either the outside or inside of themember 12, as desired, without alteringthe effect, also that the memberscan be of an'y curvatureor depth.

It will be noticed that my lens consists of two members only, that theyare ground in such 'a manner that the lens can be kept thin and light,and'moreover that it is'a very simple matter to manufacture the lens, sothat an'ordinary person skilled in the art can make it very easily,whereas in many of the lenses comprising a multiplicity of parts wit-hspecial grindings for the various members or segments, it is anexceedingly difficult matter to make the lens. It will be furtherobserved that where more than two parts are used in a complete lens, itrenders 1. A bifocal lens comprising two members 7 of essentially thesame superficial size, the close VlSlOIl member belngcomplete, and theopposite member having a sectlon removed to expose a clear section orsegment of the close vision member.

' 2. As an improved article of manufacture, a bifocal lens comprisingtwo combined members, one member being complete and the opposite memberbeing of substantially the same superficial size as the complete memberbut having a section removed .t-o-expose a corresponding portion of thecomplete member, and leaving the incompletemember overhanging thecomplete member. 3. A bifocal lens for glasses and spectacles,comprising two combined members of essentially the same circumferenceand'prin-' cipal axes, each adapted to be straddled-.lb'y a stud strap,one member constituting the close vision glass being complete, and 'thesecond or .overlapping member having a portion removed to expose a clearsection of the' first or close vision member.

4. A bifocal lens comprising two members, one member being complete, thesecond 'or overlapping member being incomplete so as to expose a clearsegment of the first or close vision member, and the two members beingcombined to produce the desired distance vision.

ANDREW JAY GROSS.

Witnesses: i

JOHN HERRMANN, JAMES R. R. MoEwnN.

